Microalgae cultures using sealed vertical photobioreactors

ABSTRACT

A microalgae culture broth producing system includes a device for culture broth sterilization using a micro bubble generator, an air compression and pressure equalization device for the injection of carbon dioxide and oxygen in the atmosphere into the culture broth. The system also includes an air chilling device to maintain suitable culture broth temperature when water temperature is too high, an automatic carbon dioxide supply device to promote photosynthesis, and a sealed vertical photobioreactor to block out pollutants and increase dissolved carbon dioxide and oxygen concentration. The system further includes a high-efficiency harvesting device using hollow fiber membranes, and a hot air drying device using the waste heat generated by air compression.

FIELD OF THE INVENTION

The present invention relates to a device for the efficient culture andharvesting of microalgae, and a method for air purification and thebiological treatment and purification of nitrogen and phosphorus insewage, which is organic wastewater, through fixation and conversion ofcarbon dioxide using biomass.

BACKGROUND OF THE INVENTION

Microalgae, which are photosynthesizing microorganisms, appeared on theprimitive earth 2 to 3 billion years ago. Based on their powerfulability to prosper and propagate, they converted the carbons that wereplentiful on the young Earth into organic materials throughphotosynthesis and discharged oxygen as the result of their metabolicability. They made the appearance of animals possible, and survive tothis day.

It cannot be denied that the current Earth environment is facing a gravecrisis due to the depletion of energy sources and the impact of globalwarming owing to excessive emission of greenhouse gases. Accordingly, inorder to reduce carbon dioxide emissions and the use of fossil fuels,bioenergy derived from organisms is gaining much attention as analternative energy source. It can thus be said that it is stronglynecessary for renewable, carbon-neutral biofuel to replace transportfuel, which is strongly dependent on conventional fossil fuels, in thenear future.

Bioenergy is not only easier to store than other types of renewableenergies, but can also be used directly in internal combustion engines.It can be mixed and used with normal diesel, and is a non-toxic,biodegradable substance. Until now, most biodiesel has been producedfrom palm oil, rapeseed oil, or other oil-rich plants. However, suchplant-derived biodiesel is met with the problem of sustainability. Forexample, to produce the annual worldwide consumption of biodiesel (about2 billion tons in 2015) from rapeseed would require about twice the landequal to the area of the Korean peninsula. Also, more than half of thetotal energy that can be produced is consumed during processing. Theseare the reasons why research and development into the production ofbiodiesel using microalgae has been gaining much attention recently.

The use of microalgae comes with many advantages. First, microalgaeexhibit productivity characteristics far superior to plants in general.The fastest-growing microalgae divide and double in number every 3hours. In addition to carbon dioxide, they can remove pollutants such asammonia, nitrates, and phosphates, making them useful in waste watertreatment as well. Also, cultured microalgae can, in addition to beingan alternative to conventional fossil fuels, produce useful naturalsubstances such as antioxidants. After extracting such substances, thebyproducts can be used as feed or fertilizer, making them a fuel sourcethat can be utilized for a wide variety of purposes.

However, there are various technical hurdles to be overcome for the massculturing of microalgae. Processes for the culture of microalgae accountfor more than 50% of total costs, followed by harvesting, concentration,drying, and separation and extraction. Existing culture methods includeregistered Korean Patent No. 10-0679989 (Raceway-type outdoor massmicroalgal culture vessel provided with seed culture vessel) andpublished Korean Patent No. 10-2012-0014387 (Photobioreactors formicroalgal mass cultures and cultivation methods using them). However,the conventional raceway pond culture system and photobioreactorsrequire a broad installation area and high initial installation costs.In the case of small raceway ponds, which have low initial facilitycosts, the forming of biofilm by the microalgae and the long culturingperiods result in lower yields. In addition, coagulants, which arechemical agents, are used for harvesting, resulting in secondary waterpollution problems. Photobioreactors, which have good yield rates, arelimited in that they are restricted to a horizontal structure in orderto induce a flow that prevents the attaching of algae to the walls. Thishorizontal structure not only makes difficult the introduction of carbondioxide in the atmosphere, but also restricts the release of thephotosynthetic product, oxygen. This oxygen poisoning limits growthproductivity.

Ultimately, it can be said that, for the commercialization ofmicroalgae, the development of a low-cost, high-energy combinationtechnology that involves low initial facility costs and reducesoperating costs by providing microalgal growth factors (light, carbondioxide, nitrogen, phosphorus, trace minerals) at low cost is urgent.

SUMMARY OF THE INVENTION

The foregoing needs are met, to a great extent, by the presentinvention, wherein in one respect a photobioreactor and method ofgrowing and harvesting microalgae are provided that in some embodimentsovercomes the disadvantages described herein at least to some extent.

An embodiment of the present invention pertains to a microalgae culturebroth producing system including a device for culture brothsterilization using a micro bubble generator, an air compression andpressure equalization device for the injection of carbon dioxide andoxygen from the atmosphere into the culture broth, and an air chillingdevice to maintain suitable culture broth temperature in response to awater temperature being higher than a predetermined maximum temperature.The system also includes an automatic carbon dioxide supply device topromote photosynthesis, a sealed vertical photobioreactor configured tocontain a culture medium inoculated with a microalgae, the verticalphotobioreactor being configured to allow light into the culture medium,block out pollutants and increase dissolved carbon dioxide and oxygenconcentration, a high-efficiency harvesting device using hollow fibermembranes, and a hot air drying device using the waste heat generated byair compression.

Another embodiment of the present invention pertains to a method for airand water purification and fixation or conversion of carbon dioxide withbiomass includes the method steps of supplying air and water to bepurified to a microalgae culture broth producing system. The microalgaeculture broth producing system includes a device for culture brothsterilization using a micro bubble generator, an air compression andpressure equalization device for the injection of carbon dioxide andoxygen from the atmosphere into the culture broth, and an air chillingdevice to maintain suitable culture broth temperature in response to awater temperature being higher than a predetermined maximum temperature.The system also includes an automatic carbon dioxide supply device topromote photosynthesis, a sealed vertical photobioreactor configured tocontain a culture medium inoculated with a microalgae, the verticalphotobioreactor being configured to allow light into the culture medium,block out pollutants and increase dissolved carbon dioxide and oxygenconcentration, a high-efficiency harvesting device using hollow fibermembranes, and a hot air drying device using the waste heat generated byair compression.

There has thus been outlined, rather broadly, certain embodiments of theinvention in order that the detailed description thereof herein may bebetter understood, and in order that the present contribution to the artmay be better appreciated. There are, of course, additional embodimentsof the invention that will be described below and which will form thesubject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of embodiments inaddition to those described and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein, as well as the abstract, are for thepurpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the facilities and equipment forefficient microalgae culturing according to the present invention.

FIG. 2 shows front and rear views of the greenhouse for microalgaeculturing according to the present invention.

FIGS. 3A and 3B are left and right sides views of the greenhouse formicroalgae culturing according to the present invention.

FIG. 4 is a cross-sectional view of the greenhouse for microalgaeculturing according to the present invention.

FIG. 5 is a first perspective view of the greenhouse installed formicroalgae culturing according to the present invention.

FIG. 6 is a second perspective view of the greenhouse installed formicroalgae culturing according to the present invention.

FIG. 7 is a third perspective view of the greenhouse installed formicroalgae culturing according to the present invention.

FIG. 8 is a structural diagram of the micro bubble generating device forsterilization of culture broth according to the present invention.

FIG. 9 is an illustration of the micro bubble generating deviceinstalled for sterilization of culture broth according to the presentinvention.

FIG. 10 is a first illustration of the culture broth and air (carbondioxide and nitrogen) supply pipes according to the present invention.

FIG. 11 is a second illustration of the culture broth and air (carbondioxide and nitrogen) supply pipes according to the present invention.

FIG. 12 is a first illustration of the air compressor installedaccording to the present invention.

FIG. 13 is a second illustration of the air compressor installedaccording to the present invention.

FIG. 14 is an illustration of the tank and air chilling device forcompressed air pressure regulation installed according to the presentinvention.

FIG. 15A is an illustration of the automatic carbon dioxide supplydevice installed and FIG. 15B is an illustration of a control panel ofthe automatic carbon dioxide supply device according to the presentinvention.

FIG. 16 is a side view of the vertical photobioreactor according to thepresent invention.

FIG. 17 is a perspective view of the vertical photobioreactor installedaccording to the present invention.

FIG. 18 is an illustration of the air pressure regulating deviceinstalled on the vertical photobioreactor according to the presentinvention.

FIG. 19 is a second perspective view of the vertical photobioreactorinstalled according to the present invention.

FIG. 20 is a third perspective view of the vertical photobioreactorinstalled according to the present invention.

FIG. 21 is a block diagram of the vertical photobioreactor according tothe present invention.

FIG. 22 is a daily growth graph for the vertical photobioreactoraccording to the present invention.

FIG. 23 is a monthly growth graph for the vertical photobioreactoraccording to the present invention.

FIG. 24 is a front view of the hollow fiber membrane microalgaeharvesting device according to the present invention.

FIG. 25 is a side view of the hollow fiber membrane microalgaeharvesting device according to the present invention.

FIG. 26 is an illustration of the hollow fiber membrane microalgaeharvesting device installed according to the present invention.

FIG. 27 is a photo of the results of operation of the hollow fibermembrane microalgae harvesting device according to the presentinvention.

FIG. 28 is an illustration of the microalgae drying device installedaccording to the present invention.

FIG. 29 is a photo of the inside of the microalgae drying deviceinstalled according to the present invention after drying.

FIG. 30 shows photos of the microalgae drying device according to thepresent invention prior to and after (right side) drying.

FIG. 31 is an illustration of the automatic control system for thegreenhouse installed according to the present invention.

FIG. 32 is a graph showing density of cells as a function of growthtemperature according to the present invention.

FIG. 33 is a graph showing density of cells as a function of growthillumination according to the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention relate to a microalgae culturebroth producing system having a device for culture broth sterilizationusing a micro bubble generator, an air compression and pressureequalization device for the injection of carbon dioxide and oxygen inthe atmosphere into the culture broth, and an air chilling device tomaintain suitable culture broth temperature when water temperature istoo high. The system also includes an automatic carbon dioxide supplydevice to promote photosynthesis, a sealed vertical photobioreactor toblock out pollutants and increase dissolved carbon dioxide and oxygenconcentration, a high-efficiency harvesting device using hollow fibermembranes, and a hot air drying device using the waste heat generated byair compression. Additional embodiments relate to a method for air andwater purification and fixation or conversion of carbon dioxide usingthe microalgae culture broth producing system described herein.

According to embodiments of the present invention, nitrogen andphosphorus-rich waste water from sewage treatment plants can besterilized using a micro bubble generator (sterilizer) and used inmicroalgae culture broth to culture microalgae which is passed through ahollow fiber membrane to harvest only the biomass (microalgae), afterwhich the purified water is discharged into rivers or re-sterilizedthrough the micro bubble generator and reused in culture broth to bothsave costs and improve the water environment.

The air pressurization and equalization device compresses carbondioxide, oxygen, and nitrogen, etc. in the atmosphere and supplies theseat a constant pressure into the photobioreactors, not only providingfactors necessary for microalgae growth but also improving the airenvironment. The sealed vertical photobioreactor increases theinfiltration rate of light, an element of photosynthesis, seals outcompetitor species or contaminants in the atmosphere, allows the easydissolving of the foregoing growth factors of carbon dioxide, etc., anddischarges oxygen, the metabolic product of photosynthesis, through adischarge pipe located on the top of the photobioreactor.

By using wastewater rich in nitrogen and phosphorus, and airbornepollutants such as carbon dioxide in the atmosphere as growth factorsfor microalgae, costs can be saved and the environment can be protected.In addition, the simple method of microalgae culturing and harvestingallows for daily harvesting at high concentrations and high purity.

Technical Problem: Until now, chlorine-based oxidizers (slightly acidicsodium hypochlorite, etc.) have been used for sterilization, which isthe core step in the treatment of raw culture broth for microalgaeculturing. However, such substances are not eco-friendly, and moreeconomically feasible technologies which can do away with the productionof harmful secondary byproducts such as trihalomethanes (THM) andhalogenic acetic acid (HAA) need to be developed.

It is necessary to develop facilities that can maximize microalgaeproduction through optimization of growth conditions, comprising aculturing device able to culture various types of microalgae throughoutthe year at low cost and high efficiency without contamination byindigenous microalgae, a device able to harvest this microalgaeffectively, and other equipment such as pressurized air generators andpipes for the supply and harvesting of culture broth which can supportthese devices.

In order to maximize productivity, BATCH TYPE (method in whichinoculation is followed by batch harvesting when peak growth is reached)methods such as the conventional raceway pond culture system orphotobioreactor should be avoided. The method should allow forcontinuous daily harvesting to maintain high growth density and theoptimization of growth conditions such as lighting and nutrition.

Using such technologies, other technologies such as devices which purifyair through the biomass conversion of carbon dioxide, and devices thatpurify waste water by biologically treating the large amounts ofnitrogen and phosphorus contained within, can be developed.

Technical Solution: To achieve the abovementioned objectives, thepresent invention provides a vinyl greenhouse in which allculture-related equipment is contained, to allow for year-roundculturing regardless of climate. As for the method for removal ofindigenous microalgae or pathogens in waste water and the sterilizationof the vertical photobioreactor, use of micro bubbles in the raw culturebroth causes solids in the water to rise to the surface for effectiveremoval, and the introduction of ozone, a strong oxidizer, into the rawwater causes the dissolved ozone and bubbles in the water to spread anddrift in the water until water pressure causes them to burst. Thehydroxyl radicals (OH⁻) that are produced when the ozone molecules arewithin the bubbles purify and completely sterilize the raw culturebroth, replacing conventional chlorine-based oxidizers.

Carbon dioxide, nitrogen, and oxygen, which are key elements ofphotosynthesis, are compressed to 10 bar using an air compressor andpassed through multiple stages of microfilters to filter out competingspecies or pathogens in the air. This purified compressed air is fed 24hours a day through pipes into the bottom of each photobioreactor.During day hours with sunlight, the carbon dioxide that exists at aconcentration of 350 ppm in the air is used for photosynthesis, andduring night hours, when there is no light, the oxygen in the atmospherethat is required for respiration by the microalgae is supplied,providing optimal growth conditions. Also, a vertical photobioreactor isprovided, meaning that the compressed air that is introduced through thelower pipes rises to the surface, forming bubbles, and causing naturalripples. This not only prevents the microalgae from attaching themselvesto the wall surfaces, but also induces the dissolving of carbon dioxideand nitrogen, etc. in the atmosphere into the culture broth. Under theseoptimal growth conditions, rapid growth takes place. When theconcentration reaches its peak, at which sunlight is blocked out, ½ isharvested at 24 hours to maintain a culture concentration optimal forlight absorption. The photobioreactor is replenished with an amount ofculture broth equal to the amount harvested, along with the nutrientsnecessary for growth.

Through the foregoing method, high-density culturing is possibleyear-round regardless of climate, even in limited space.

Effects of embodiments of the invention: The freely available carbondioxide and nitrogen, etc., in the environment are used, improving theatmospheric environment, and the phosphorus and nitrogen in treatedwaste water can be used in the culture broth to achieve waterpurification effects.

By using pollutants as resources in the culture of microalgae, apositive circulation of resources can be induced, and economicfeasibility can be secured by minimizing production costs.

While the lowering of productivity due to culture broth contaminationhas been the greatest hurdle to microalgae culturing until now,eco-friendly ozone and hydroxyl radical (OH—) sterilization overcomethis obstacle, and a sealed structure for the photobioreactors protectsthe cultures from competing algae or pollutants in the air, providingoptimal growth conditions.

The vertical structure facilitates harvesting and the supply of culturebroth, allowing for harvesting at 24 hours and optimal light conditionsto maximize productivity.

The harvested microalgae is passed through a hollow fiber membrane toseparate the microalgae from the water. The water is then sterilizedwith a micro bubble generator/sterilizer, and reused in culture broth.The concentrated microalgae is dried out using the warm air dischargedfrom the compressor.

A microalgae growth and harvesting system 10 according to embodiment ofthe present invention is shown in FIG. 1. As shown in FIG. 1, themicroalgae growth and harvesting system 10 includes a greenhouse 101, aquality control room 102 and a freezer compartment 103. The microalgaegrowth and harvesting system 10 also includes a sterilizer 200 such as amicro bubble generator for generating a supply of pressurized ozone tosterilize incoming growth media.

The present invention relates to a method for continuous and economicmass production of microalgae-derived biomass without contamination.

Microalgae are primary producers that produce organic compounds throughphotosynthesis. Their product, biomass, is a substitute for the liquidenergy of fossil fuels, while their pigment assimilation substances,with the powerful antioxidative abilities, are capable of producinguseful eco-friendly natural substances such as drugs. Microalgae areemerging as an alternative to various petrochemical products, and, beinga nutritionally complete food, are being used for food or health foodsupplements. After extracting these useful substances, the byproductscan be used as animal feed or fertilizer. Recently, organic microalgaebyproducts are being used to promote plant growth and for pestprevention.

The success of plants that mass produce microalgae is determined by thehandling of water (culture broth), the most important of the fourelements (water, carbon dioxide, light, nutrients) required for theculture of microalgae.

Groundwater, lakes, rivers and seawater are the main sources for thewater in microalgae culture broth. However, due to rapidindustrialization in the 21st century, serious air, water and soilpollution have resulted. This means that raw water cannot be used as-is,but must be completely sterilized to remove any foreign debris, toxins,residual antibiotics and microbes, etc., in the water.

Until now, chlorine-based oxidizers (slightly acidic sodiumhypochlorite, etc.) have been used for sterilization, which is the corestep in the treatment of raw culture broth for microalgae culturing.However, such substances are not eco-friendly, and the production ofharmful secondary byproducts such as trihalomethanes (THM) and halogenicacetic acid (HAA) have been a hurdle to the mass culturing ofmicroalgae. Accordingly, the sterilizer 200 uses microbubbles in the rawculture broth to effectively remove solids in the water. The adding ofozone, a strong oxidizer, into the raw water causes the dissolved ozoneand bubbles in the water to spread and drift in the water until waterpressure causes them to burst. The hydroxyl radicals (OH—) that areproduced when the ozone molecules within the bubbles purify andcompletely sterilize the raw culture broth.

The composition and performance of the micro bubble generator for thetreatment of the microalgae culture broth are as follow: 1)Composition;—Pump: 5˜10 tons/hour—Gases introduced: Air, oxygen, ozone;and 2) Performance;—bubble size: <20 micrometers—Dissolved gasconcentration: >80%—Allowable size of solids: <5 mm.

The microalgae growth and harvesting system 10 includes a microalgaeculture medium feeder apparatus 301, an air/CO₂ feeder apparatus 302,one or more compressors 401 that generates compressed air, a highpressure tank 402 to store the compressed air from the compressor 401,an air chiller 403 to cool compressed air and a vertical photobioreactorsystem 500. In a particular example, the photobioreactor system 500includes one or an array of vertically arranged photobioreactors(V-PBR).

Selected and incubated microalgae, cultured up to 50 million cell/ml andup to 200 L volume, will be filled into one vertical photobioreactor(V-PBR) unit. One unit of vertical photobioreactor (V-PBR) comprises 20tubes and total filled cultural water volume is about 2,000 L. Each tubesize is Φ14 mm×4,000 mm and material made from polycarbonate or othertransparent polymers. Each V-PBR unit can be operated independently oras a photobioreactor system 500.

In one embodiment, after filling between 170 L to 200 L of incubatedmicroalgae as a seed into the V-PBR unit, then fill about 1,300 L toabout 1,800 L of cultural water through the microalgae culture mediumfeeder apparatus 301 and air/CO₂ feeder apparatus 302. Before fillingcultural water into the V-PBR unit, cultural water must be sterilized ina tank using sterilizer 200. In one embodiment, the sterilizer 200 is amicro bubble generator using oxygen and ozone gas as the bubble gas. Thesterilizer 200 contains oxygen and ozone generator in a console box (seeFIG. 8) and it generates oxygen by using air and the generated oxygen inturn generates ozone. The sterilized cultural water can be stored forabout 24-48 hours in a tank before use in order to minimize dissolvedoxygen and ozone level in cultural water.

The purified and sterilized culture broth is introduced into thevertically arranged photobioreactors 500 by being pumped through theconnected microalgae culture medium feeder apparatus 301.

The vertical photobioreactors 500 are inoculated with thehigh-concentration microalgae cultured in the intermediate reactor(microalgae culture medium feeder apparatus 301) through pipes installedon the bottom of the vertical photobioreactors, after which anappropriate amount (0.5% of the raw culture broth) of nutrients isintroduced.

The air compressed by the air compressor 401 is temporarily stored in apressure regulating (high pressure tank) device 402 (up to 10 barpressure). Using the micro filters (e.g., lx 5 micron, 1× 1 micron, or1× 0.1 micron) in the air chiller 403, any file dust particles ofindigenous microalgae (competing microalgae or pathogens, etc.) arefiltered out at the set air pressure.

The purified air (including carbon dioxide, nitrogen and oxygen) ismoved through the air/CO₂ feeder apparatus 302 and is purified a secondtime when passing through the filter of the fine control deviceinstalled on the bottom of the vertical photobioreactors 500.

The air that is introduced forms air bubbles, rising to the top andcreating ripples. This keeps the microalgae from attaching to the wallsof the vertical photobioreactors 500 while growing, and blocking outsunlight. In addition, the culture broth moves horizontally andvertically, increasing opportunities for contact with light (growthfactors) and promoting growth.

Some of the benefits of the air supply include supplying carbon dioxide,oxygen, preventing biofilm formation on the surface of the tube, evendispersion of microalgae, and controlling the cultural watertemperature. It should be noted that there is about 0.03% (which is toohigh) of carbon dioxide in the air and by supplying air into the V-PBR'stube, the carbon dioxide can be diluted in the water and helpmicroalgae's photosynthesis activity in daylight. In another embodiment,the carbon dioxide can be in liquid form. At night, microalgae needoxygen for their respiration. By supplying air at night, about 23% ofoxygen in the air can be diluted in the water and helps the respirationby the microalgae. As the air is introduced, the air bubbles aretraveling to the right, left and vertically up to the top of the V-PBR.These movements can help to mix the microalgae evenly in the water andincrease their light contact ratio. In microalgae cultural environment,the water temperature is the most sensitive factor. By inserting airtemperature control, cool and warm, water temperatures can be controlledmore precisely.

Microalgae needs food for growing. As their food, inorganic nutrientssuch as nitrogen, phosphorus and minerals can be supplied and its totalvolume is about 0.2% to about 0.5% of total cultural volume. It can besupplied to V-PBR unit individually through the air/CO₂ feeder apparatus302 or through mixing with microalgae culture medium feeder apparatus301.

Once the peak (10,000,000-50,000,000 cells/ml) is reached, ½ of theculture broth is recovered (harvested) at 24 hour intervals through themicroalgae culture medium feeder apparatus 301 and/or the air/CO₂ feederapparatus 302. This allows for the optimum culture competition forabsorption of light for photosynthesis to be maintained. Beforeharvesting, cell number and size can be monitored and cell shape andstatus can be analyzed though equipment such as illuminator, salimeter,and the like. Harvested cultured water can be sent to 0.1 micron size ofthe hollow fiber membrane harvester 600 and it will be separated anddelivered to two different harvest tanks 900. One tank 900 is forfiltered cultured water without microalgae biomass and the other tank900 is for cultured water with microalgae biomass. The verticalphotobioreactor is replenished with an amount of ozone-sterilizedculture broth equal to the amount harvested, adding the nutrients thatare necessary for growth. In other words, refill the V-PBR with about25% of harvested and separated cultured water and about 25% of normalwater, which was sterilized using sterilizer 200 at least 24 hours ago.Once all tubes of the V-PBR are refilled, supply microalgae food(nitrogen, phosphorus and minerals) and air as the initial microalgaeinoculation process.

The present invention, as described in the embodiments, allows formaximum productivity by repeating this culturing method. The culturebroth recovered through the microalgae culture medium feeder apparatus301 (high-density microalgae) is passed through a hollow fiber membraneseparator 600 that employs the reverse osmosis principle to harvest thewater and microalgae separately. The water is then purified andsterilized through the micro bubble generator 200 and reused in thephotobioreactors 500. The harvested high-density microalgae is dried ina dryer 700 that uses the heat that is generated during air compression.

A control panel 800 is utilized to oversee the operation of themicroalgae growth and harvesting system 10. The control panel 800 isconfigured to control the cultural water temperature through the airbubble air temperature generated by air chiller 403. The control panel800 can also control the pH level of the cultural water in the tubesthrough the use of the carbon dioxide supply. Further, the control panel800 can control and monitor the air bubble status (size, speed throughwater, etc.) through the air supply valve on the air compressor 401.

FIG. 2 shows front and rear views of the greenhouse 101 for microalgaeculturing according to the present invention and FIGS. 3A and 3B areleft and right side views of the greenhouse 101 for microalgae culturingaccording to the present invention. FIG. 4 is a cross-sectional view ofthe greenhouse 101 for microalgae culturing according to the presentinvention showing an auto ceiling opener/closer 110, a shade 112, ashade drive motor 114, a window drive motor 116, and window 118 operatedby the window drive motor 116.

FIG. 5 is a first perspective view of the greenhouse 101 installed formicroalgae culturing according to the present invention showing thevertical photobioreactors 500 in a disassembled state. FIG. 6 is asecond perspective view of the greenhouse 101 installed for microalgaeculturing according to the present invention showing the area in whichthe photobioreactor 500 is to be assembled. FIG. 7 is a thirdperspective view of the greenhouse 101 installed for microalgaeculturing according to the present invention showing the assembledphotobioreactor 500 installed in the greenhouse 101.

FIG. 8 is a structural diagram of the micro bubble generating device 200for sterilization of culture broth according to the present inventionshowing the sterilizer 200 includes an oxygen generator 210, an ozonegenerator 212, a pump 214 and a float tank 216. Air 205 from theenvironment is taken into the micro bubble generating device 200.Culture broth in the form of raw water or sewage is placed in the floattank 216 and ozone is bubbled through the culture broth from below.Excess ozone is collected from the top of the float tank 216 and fedback to the bottom of the float tank 216.

FIG. 9 is an illustration of the micro bubble generating device 200installed for sterilization of culture broth according to the presentinvention showing the connection to the float tank 216

FIG. 10 is a first illustration of the culture broth and air (carbondioxide and nitrogen) supply pipes according to the present invention.As shown in FIG. 10, the photobioreactor 500 is supplied with air/CO₂from the compressor 401 via the line of the air/CO₂ feeder apparatus 302and the photobioreactor 500 is supplied with culture media from a pump510 via the line of the microalgae culture medium feeder apparatus 301.FIG. 11 is a second illustration of the culture broth and air (carbondioxide and nitrogen) supply pipes of the microalgae culture mediumfeeder apparatus 301 and of the air/CO₂ feeder apparatus 302 accordingto the present invention.

FIG. 12 is a first illustration of the air compressor 401 installedaccording to the present invention and FIG. 13 is a second illustrationof the air compressor 401 installed according to the present invention.

FIG. 14 is an illustration of the high pressure tank 402 and airchilling device, air chiller 403 for compressed air pressure regulationinstalled according to the present invention. Also shown in FIG. 14 is astorage tank 410 for culture media. FIG. 15A is an illustration of theautomatic carbon dioxide supply device 412 installed according to thepresent invention, and FIG. 15B is an illustration of a control panel ofthe automatic carbon dioxide supply device 412.

FIG. 16 is a side view of the vertical photobioreactor 500 according tothe present invention and FIG. 17 is a perspective view of the verticalphotobioreactor 500 installed according to the present invention. FIG.18 is an illustration of an air pressure regulating device 520 installedon the vertical photobioreactor 500 according to the present inventionand FIG. 19 is a second perspective view of the vertical photobioreactor500 installed according to the present invention. FIG. 20 is a thirdperspective view of the vertical photobioreactor 500 installed accordingto the present invention. FIG. 21 is a block diagram of the verticalphotobioreactor 500 according to the present invention. As shown in FIG.21, air/CO₂ is supplied via the compressor 401, tank 402, and airchiller 403. Media is supplied via the tank 410. The microalgae is grownin the vertical photobioreactor 500 and collected in a harvest tank 900.

FIG. 22 is a daily growth graph for the vertical photobioreactoraccording to the present invention and FIG. 23 is a monthly growth graphfor the vertical photobioreactor according to the present invention.

FIG. 24 is a front view of the hollow fiber membrane microalgaeharvesting device 600 according to the present invention and FIG. 25 isa side view of the hollow fiber membrane microalgae harvesting device600 according to the present invention. In general, the hollow fibermembrane microalgae harvesting device 600 concentrates the culturedmicroalgae by passing the culture past hollow fibers at high pressure.The openings in the fibers are too small for the microalgae to passthrough so the microalgae is concentrated. FIG. 26 is an illustration ofthe hollow fiber membrane microalgae harvesting device 600 installedaccording to the present invention.

FIG. 27 is a photo of the results of operation of the hollow fibermembrane microalgae harvesting device 600 according to the presentinvention. As shown in FIG. 27, the raw culture media (far right) isfiltered to produce concentrate (middle container) and supernatant (farleft).

FIG. 28 is an illustration of the microalgae drying device 700 installedaccording to the present invention. FIG. 29 is a photo of the inside ofthe microalgae drying device 700 installed according to the presentinvention after drying. FIG. 30 shows photos of the concentratedmicroalgae before (left bucket) and after (right bucket) drying in themicroalgae drying device 700 according to the present invention. FIG. 31is an illustration of the automatic control system 800 for thegreenhouse 101 installed according to the present invention.

In the following, an embodiment of the present invention is describedwith reference to the exemplary embodiments thereof. The embodimentsrepresent the results of a 1-month test run of the present invention.The embodiments contained herein are exemplary embodiments of thepresent invention, and it shall be obvious to a person having ordinaryskill in the art that these embodiments are not intended to restrict theprotective scope of the present invention to these embodiments.

Examples

In the present experiment, the cold water marine microalgaeNannochloropsis sp. was used in an outdoor growth experiment with 2 tonsof culture broth for the purpose of evaluating the productivity of thehigh-efficiency vertical photobioreactor invented by the presentinventor. In the experiment, which was carried out for 1 month, averagedaily productivity was 0.953 g/L in the culture with 0.1% CO₂introduced, while productivity was 0.574 g/L when only air wasintroduced. As for temperature distribution, the range was from aminimum of 20° C. to a maximum of 31° C. It was shown that there was nosignificant difference in productivity according to temperature withinthis range. Light was shone at a brightness of 5,000 to 40,000 Lux, andit was found that the intensity of the light and the growth of themicroalgae were very closely related. Meanwhile, it was found that themethod of microalgae culturing by pressurized in-reactor flotationattempted in the present experiment was highly effective.

The strain used in the present experiment was Nannochloropsis sp.(KMMCC-290) from the Korean Marine Microalgae Culture Center, and CONYWYculture base was used to culture the strain (Cuillard and Ryther, 1962).The strain was liquid and solid cultured under 25° C. temperatureconditions, and was stored or used for inoculation.

The basic composition of the experimental device for outdoor culturetesting is as follows: photobioreactors, air compressor, carbon dioxideinjector, culture broth mixer and culture broth harvester shown in FIG.21. The photobioreactors were connected to a special transparentpolycarbonate pipe 4,000 mm long with a diameter of 140 mm, with 20photobioreactors attached to each of 2 lines. 2,000 L seawatersterilized using the micro bubble device (OH⁻) was injected. Each linewas inoculated with 200 L, which is 1/10 of the 2,000 L total amount ofculture broth, to a concentration of about 5.0×10⁷ cells per mL. Eight(8) hours after inoculation, sterilized cow's urine as a source ofnitrogen and other inorganic nutrients was injected to a concentrationof 0.5%, and culturing was continued. In one line, air (including 0.03%carbon dioxide) was supplied through the air compressor, and in theother line, 0.1% liquefied carbon dioxide was mixed in.

The inoculated culture broth was cultured for the first 5 days afterinoculation in an optimized state with the air compressor valve wasadjusted so that the culture broth would not reach the connecting PVCpipes attached to the top of each culture pipe. On the sixth day, 50% or1,000 L of the culture broth was discharged through the lower pipes, andharvested. Then each line was replenished with 500 L of new culturebroth, an amount equivalent to the culture broth discharged from each.This was repeated every 24 hours, with the photobioreactors operatedcontinuously for 30 days.

The 1,000 L of harvested high-concentration culture broth was furtherconcentrated using a hollow fiber membrane, and after about 30 minutes,the concentrated microalgae was desalinated 2 times with fresh water.The desalinated microalgae was dried using an oven dryer to a moisturecontent of 4% of less, after which the total dry cell weight was foundto determine the total cell mass.

A certain amount of the specimens collected from each of the culturebroths was diluted, and the cell count was measured using ahemocytometer. The measured cell count was divided by the cell mass togive the dry cell weight per cell. Note that intensity of illuminationduring culturing was measured using a portable Lux meter capable ofmeasuring between 600 and 300,000 Lux. Units are shown in Lux.

As shown in FIG. 22, the number of cells prior to addition to inorganicnutrients in the line (Line A) injected with air only and the lineinjected with a mixture of air and 0.1% carbon dioxide (Line B) wasfound to be 0.55 to 0.60×10⁷ cells indicating a suitable initialdilution rate. From the second day after inoculation until harvesting,the cell count approximately doubled in both lines, reaching 2.6×10⁷cells and 4.8×10⁷ cells, respectively, on the 5th day after inoculation,one day prior to harvesting. As was expected, the growth rate of thecells in Line B with the injected carbon dioxide was higher than in LineA. The pre-harvest cell count of Line B was almost double that of LineA.

Harvesting of cells was attempted from the 6th day after inoculationonward. It was determined that the culture broth would be extracted atthis time based on results from previous experiments wherein the peakexponential growth rate was reached between 120 and 150 hours.Accordingly, the culture broth was extracted every 24 hours forharvesting from the 6th day onward. The amount of culture brothextracted at this point was 1,000 L, or 50% of the 2,000 L total. Thiswas because the optimal culture state was reached 24 hours afterreplenishment with new culture broth immediately following 50%extraction. The concentration of cells within the photobioreactorsimmediately prior to extraction on the 6th day was 3.5×10⁷ cells and 60.1×10⁷ cells per 1 ml for Line A and Line B, respectively.

After initial inoculation, 1,000 L of culture broth was extracted fromthe 6th day onward, on which it was judged that the peak of theexponential growth phase was reached. As shown in FIG. 23, culturingcontinued for an additional 25 days, replenishing the photobioreactorswith the same amount of culture broth extracted. To analyze the growthrate, the cell counts were measured in the culture broth immediatelyafter inoculation and immediately prior to extraction. By finding thecell count and dry cell weight of the extracted microalgae, the averagedaily cell count and growth rate, etc., were analyzed as shown in FIG.23 and Table 1.

TABLE 1 Specific Growth Rate, Average Cell Number, and Average DryWeight of Cells in A & B Lines. Average cell Average dry Specific numberper day cell weight per day growth rate (k) A Line 3.83 × 10⁷ cells/ml0.574 g/L 0.047 B Line 6.35 × 10⁷ cells/ml 0.953 g/L 0.055

For Line B, with 0.1% CO₂ injected, the daily average cell count per 1ml immediately prior to extraction was found by dividing the total cellcount over 25 days, giving a value of 6.35×10⁷ cells/ml. Meanwhile, thegrowth rate inside the photobioreactors was found using the followingequation, which applies to the growth rate of cells in the exponentialgrowth phase.

In the equation for cell growth rate: N=No2n, N it the cell count aftert hours have passed, and NO is the initial cell count. The lower case nis the number of generations within t hours. Substituting Log functionsin the equation above gives the following: Log N=Log N0+nLog 2. Thetotal generation count, n, becomes Log N−Log N0+Log 2 (0.301). Here, theinitial cell count NO is the total cell count within the 2-tonphotobioreactor which has been replenished with an equal amount of newculture broth after 100 L of high-concentration pressurized flotationculture broth has been extracted. The cell count N after 5 hours becomesthe total cell count when 24 hours have passed after the addition ofculture broth, immediately prior to extraction.

In Line B, the initial cell count and the total cell count immediatelyprior to extraction are as follow, and accordingly, the total number ofgenerations, n, becomes approximately 4.40 generations. Where theinitial cell count N0=3.0×10⁶ cells/ml. The cell count immediately priorto harvesting N=6.35×10⁷ cells/ml. The total generation count n=LogN−Log N0÷0.301≈4.40

Meanwhile, the specific growth rate of cells, k, was found to have avalue of 0.301/g, were g is doubling time. The doubling time is thetotal culturing time divided by the number of generations. The g valuefor Line B, which is 24 hours divided by the generation count of 4.4,becomes approximately 5.45 hours. Accordingly, the specific growth rateK for Line B was found to have a value of approximately 0.055, which is0.301 divided by 5.45 hours. Where g=t/n=24 hours/4.4 generations 5.45and where k=0.301/g=0.301/5.45≈0.055.

For Line A, injected with air only, the initial cell count afterdilution was measured at 2.8×10⁶ cells/ml, giving a total generationcount of approximately 3.77 generations, approximately 6.37 hours'generation time, and a value of 0.047 for the specific growth rate k.

Meanwhile, the average daily dry cell weight for Line B found by drying100 L of the harvested cells was calculated to be 1,800 g. Diving thisby the total cell count gave a dry cell weight of 0.015 μg/cell.Multiplying this by the average daily cell count of 6.35×10⁷cells/ml×2.000 L gave an average daily cell mass per liter of 0.953 g/Lfor Line B. The cell mass for Line A, which was not supplied with carbondioxide, was calculated to be 0.574 g/L.

The present experiment was carried out in Gangneung, S. Korea, over themonth of September 2014. The minimum air temperature in the area wasaround 20° C., with a maximum daytime temperature exceeding 30° C. Inorder to keep the temperature of the culture broth between 25° C. and30° C., chilled air was injected when the temperature of the culturebroth exceeded 29° C. to regulate the maximum temperature to no morethan 30° C. During the experimental period, the culture broth recorded aminimum temperature of 20° C., reaching a maximum temperature of 31° C.As seen in FIG. 32, temperature changes during the experimental perioddid not have a large impact on cell growth. This is judged to be becausethe range of temperature variation was small, at 25° C.±5° C.

Among the environmental factors impacting the growth of microalgae, therole of light is very important. The results of the present experimentalso gave results demonstrating this influence of light. AroundSeptember 2014, when the experiment was carried out, the weather inGangneung was sunny about half of the time, and cloudy the rest. Onrainy or cloudy days, the intensity of illumination was generallybetween 5,000 and 30,000 Lux, while 300,000 Lux was exceeded during thedaytime on sunny days. Excessively intense light can stop photosynthesisdue to light saturation, and radiant heat can cause the temperature ofthe culture broth to increase, suppressing growth of the cold watermarine organism Nannochloropsis sp. Therefore, a shade was installed onclear days with intense sunlight, keeping light intensity between 20,000to 30,000 Lux.

Observation of microalgae growth from the 6th day after inoculation tothe 30th day, when the experiment ended, showed that there was a veryclose correlation between light intensity and algal growth, as seen inFIG. 33. Also, it can be known that the growth rate had a steeperincline when 0.1% carbon dioxide was injected than when only oxygen wasinjected.

The hydroxyl radicals (OH—) in the present experiment, which dissolvetoxins within the raw culture broth, can be reused. It is expected thatthe sealed vertical photobioreactor will be an economically feasible,technologically advanced and environmentally friendly system formicroalgae culturing and harvesting.

Meanwhile, it was discovered in the present growth rate experiment thatlight and carbon dioxide acted as key elements of growth, according towhich further research will be conducted into the optimum concentrationof carbon dioxide for growth and the impact of light intensity anddifferent light wavelengths on growth in order to further improveproductivity.

A preferred embodiment of the present invention has been described indetail in the foregoing, and the substantial scope of the presentinvention will be defined by the appended claims and equivalentsthereof.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

PCT/US2017/040760, having an international filing date of Jul. 5, 2017,is incorporated by reference herein in its entirety.

1-14. (canceled)
 15. An apparatus for cultivation of microalgae in aculture broth, comprising: a device for culture broth sterilizationusing a micro bubble generator; an air compression and pressureequalization device for injection of carbon dioxide and oxygen fromatmosphere into a culture broth; an air chilling device to maintainsuitable culture broth temperature; an automatic carbon dioxide supplydevice to promote photosynthesis; a sealed vertical photobioreactorconfigured to contain a culture medium inoculated with a microalgae; aharvesting device comprising hollow fiber membranes; and a hot airdrying device.
 16. The apparatus according to claim 15, wherein the aircompression and pressure equalization device comprises a device tocompress carbon dioxide and oxygen in atmosphere to 10 bar, a device(tank) to equalize air pressure, and pipes and a gas backflow preventingdevice to inject compressed gases into the culture broth.
 17. Theapparatus according to claim 15, wherein the automatic carbon dioxidesupply device supplies liquefied carbon dioxide into the culture brothusing a pH sensor.
 18. The apparatus according to claim 17, wherein theautomatic carbon dioxide supply device automatically supplies carbondioxide when pH of a culture broth is 7.26 or higher, and automaticallycuts off carbon dioxide when pH of a culture broth is less than 7.26 ifmicroalgae is a freshwater microalgae, and automatically supplies carbondioxide when pH of a culture broth is 7.30 or higher, and automaticallycuts off carbon dioxide when pH of a culture broth is less than 7.30 ifa microalgae is a seawater microalgae.
 19. The apparatus according toclaim 15, wherein compressed gas is injected into bottom of theapparatus.
 20. The apparatus according to claim 19, further comprising adevice for control of gas pressure.
 21. The apparatus according to claim20, wherein mutual exchange and flow of culture broth among identicalconnected vertical photobioreactors is induced solely by buoyant forceof pressure-adjusted air.
 22. The apparatus according to claim 15,wherein a concentrated microalgae harvested through pipes from thephotobioreactor is passed through a hollow fiber membrane to allow forseparate harvesting of culture broth and biomass.
 23. A system forculturing microalgae, comprising: a device for culture brothsterilization using a micro bubble generator; an air compression andpressure equalization device for the injection of carbon dioxide andoxygen from the atmosphere into the culture broth; an air chillingdevice to maintain suitable culture broth temperature; an automaticcarbon dioxide supply device to promote photosynthesis; a sealedvertical photobioreactor configured to contain a culture mediuminoculated with a microalgae; a harvesting device comprising hollowfiber membranes; and a hot air drying device.
 24. The system accordingto claim 23, wherein the air compression and pressure equalizationdevice comprises a device to compress carbon dioxide and oxygen inatmosphere to 10 bar, a device (tank) to equalize air pressure, andpipes and a gas backflow preventing device to inject compressed gasesinto the culture broth.
 25. The system according to claim 23, whereinthe automatic carbon dioxide supply device supplies liquefied carbondioxide into the culture broth using a pH sensor.
 26. The systemaccording to claim 25, wherein the automatic carbon dioxide supplydevice automatically supplies carbon dioxide when pH of a culture brothis 7.26 or higher, and automatically cuts off carbon dioxide when pH ofa culture broth is less than 7.26 if microalgae is a freshwatermicroalgae, and automatically supplies carbon dioxide when pH of aculture broth is 7.30 or higher, and automatically cuts off carbondioxide when pH of a culture broth is less than 7.30 if a microalgae isa seawater microalgae.
 27. The system according to claim 23, whereincompressed gas is injected into bottom of the apparatus.
 28. The systemaccording to claim 27, further comprising a device for control of gaspressure.
 29. The system according to claim 28, wherein mutual exchangeand flow of culture broth among identical connected verticalphotobioreactors is induced solely by buoyant force of pressure-adjustedair.
 30. The system according to claim 23, wherein a concentratedmicroalgae harvested through pipes from the photobioreactor is passedthrough a hollow fiber membrane to allow for separate harvesting ofculture broth and biomass.
 31. The system according to claim 23, furthercomprising a vinyl greenhouse to ensure optimized year-round microalgaeculturing, and operating devices therefor.